1. Field of the Invention
The invention relates to a barless mold closing device for injection molding machines, having a C-shaped machine frame, on one leg of which a fixed die mounting plate is arranged and on the other leg of which an end plate is arranged. Between these legs, a movable die mounting plate can be moved longitudinally on guides with the help of a linear drive, which is supported in the end plate and the movable die mounting plate. The fixed die mounting plate and the movable die mounting plate have mounting surfaces to hold the mold halves of a molding die. The mold closing and opening force produced by the linear drive during the injection and opening process is absorbed by the machine frame.
2. Description of the Related Art
From DE 9212480 U1 and EP 0554068 A1, generic barless mold closing devices are already known, the advantage of which is that the die space between the fixed and movable die mounting plates is freely accessible. As a result, gaining access to the die and changing the die are considerably simpler than in mold closing devices with die mounting plates that are connected by bars. Furthermore, in barless mold closing devices, because of better utilization of the die mounting surface, it is possible to use larger dies in injection molding machines with a smaller closing force. In barless injection mold machines, the large closing and mold expansion forces occurring during the injection process and the mold opening forces occurring during the opening process lead to a deformation of the machine frame, which consists of a longitudinal expansion and a superimposed bending deformation, the latter of which may result in non-parallelisms at the die parting line.
In DE 9212480 U1 and EP 0554068 A1, the problem is solved by the fact that the two die mounting plates are supported horizontally and uniaxially and are tiltable, allowing plane parallelism to be maintained. In DE 9212480 U1, in order to prevent the movable die mounting plate from lifting up from the machine frame, the movable die mounting plate has a shoe which is connected to a guide rail in a positive-locking manner. The guide rail is supported either on the fixed die mounting plate in a one-sided fashion or on the machine frame. In order to ensure elastic movement between the movable die mounting plate and the guide rail, springs are arranged between the shoe and the movable die mounting plate, or the guide rail is attached to the machine frame by means of springs. The disadvantage of this solution is that when the plastic mass is injected into the cavity of the molding die, the large internal die pressure which prevails and the uniaxial bearing of the two die mounting plates may lead to a deformation of the die mounting plates in the upper and lower border regions. These deformations may be of various sizes, depending on the geometry of the mold part and the position of the cavity in the molding die. It may even be necessary structurally to locate cavities with a large surface at a wide distance from the horizontal central axis, in the external upper or lower border region of the molding die. In order to prevent an expansion of the molding die during the injection process and to ensure the production of high-quality mold parts, the die mounting plates must therefore be designed with considerably thicker walls as the size of the mounting surface increases. Furthermore, the guides for the molding dies and the movable die mounting plate as well as the bearings for the movable die mounting plate, the end plate, and the movable and fixed die mounting plates are under different loads and, as a result, are subject to rapid wear.
In EP 0554068 A1, generic designs that vary structurally are described and depicted. The end plate and the fixed die mounting plate as well as, in part, the movable die mounting plate are supported in uniaxial and articulated fashion. However, the forces arising during the production of the mold closing and opening force are absorbed chiefly by a so-called locking assembly, which consists of two plates arranged in the longitudinal direction, in which the end plate and the fixed die mounting plate are supported in an articulated fashion.
The movable die mounting plate, the fixed die mounting plate and the end plate are thereby run or supported on the machine framework. This solution has a further disadvantage, in addition to these described above, namely, that the plates arranged in the longitudinal direction for the locking assembly necessitate high additional material and cost expenditure.